Field
Aspects of the present invention generally relate to an image heating device such as a fixing unit mounted in an image forming apparatus of an electrophotographic recording type, such as a copier or a printer, or a glossing device for improving a toner image in gloss by heating a fixed toner image on a recording material again.
Description of the Related Art
As an image heating device, there is a device having a cylindrical film, a heater in contact with an inner surface of the film, and a roller forming a nip portion via the film together with the heater. When an image forming apparatus provided with such an image heating device performs continuous printing using small-sized paper, a phenomenon occurs in which temperature of a region through which sheets do not pass in a longitudinal direction of the nip portion gently increases (temperature rise in a sheet non-passing portion). If the temperature of the sheet non-passing portion becomes too high, individual parts in the device may be damaged, or if printing is performed by using large-sized paper while the temperature rise in the sheet non-passing portion is generated, high-temperature offset of toner may occur to the film in a region corresponding to the sheet non-passing portion of the small-sized paper.
As one of methods for suppressing such a temperature rise in the sheet non-passing portion, a device which switches heat generation distribution of a heater according to a size of a recording material by dividing a heat generating resistor on the heater into a plurality of groups (heat generating blocks) in a longitudinal direction of the heater is proposed (Japanese Patent Laid-Open No. 2014-59508).
When the heat generating resistor is divided into the plurality of heat generating blocks, a temperature detecting element can be arranged on each of the heat generating blocks in order to monitor abnormal heat generation of the heater.
However, as the number of the heat generating blocks increases, the number of the temperature detecting elements for monitoring the temperature also increases.